Notebooks has a built in WebDAV server (WiFi Sharing) which can be used to synchronize Notebooks on separate devices, too. To do so, follow these steps (we assume that the iPad is the server; your setup can be the other way round as well):

In Notebooks on your iPad, enable WiFi Sharing in settings and set up a WiFi user.

At the top level book, select Share This Book from the context menu.

In the view that appears, turn ON the switch Show System Files to make sure that all task data and details are transferred, too.

In Notebooks on your iPhone, change the WebDAV settings to the details given on the iPad’s Sharing info (http address, user name and password)

On your iPhone, move to the book that you would like to synchronize and select Sync from the action menu.

Now all your books, notes, tasks and documents will be synced from your iPhone to your iPad. Of course, the same procedure works in the opposite direction and between any devices running Notebooks. If you use this procedure regularly, it is best to always sync in the same direction.